Electronically scanning antenna empolying plural phase-locked loops to produce optimum directivity



y 1962 F. w. LEHAN ETAL ELECTRONICALLY SCANNING ANTENNA EMPLOYING PLURAL PHASE-LOCKED LOOPS TO PRODUCE OPTIMUM DIRECTIVITY 3 Sheets-Sheet 2 Filed Nov. 2, 1959 I A' W LEA AN WILL/AM A. Huemss INVENTORS BY M A7TO 2 EY United States Patent .0

ELECTRONICALLY SCANNING ANTENNA EM- PLOYING PLURAL PHASE-LOCKED LOOPS TO PRODUCE OPTIMUM DIRECTIVITY Frank W. Lehan, Glendale, and William R. Hughes,

Northridge, Calif., assignors to Space-General Corporation, Glendale, Califi, a corporation of (California Filed Nov. 2, 1959, Ser. No. 850,481 20 Claims. (Cl. 250-6) The present invention relates in general to the field of antennas and more particularly to an electronically scanning antenna system.

It is frequently necessary to search a portion of the sky for a particular signal source and, once having located it, to lock onto it and also follow or track it should the position of the source change with time. Thus, by way of example, it may be necessary to locate and lock onto a radio transmitter at a fixed station for the purpose of establishing communication therewith or it may be essential to find a satellite or missile travelling at high speed through space and thereafter to maintain contact with it in order to continuously receive its information signals. As is well known by those skilled in the electronic arts, antennas are the means by which these results are attained.

More particularly, it has been customary in the past to employ an antenna arrangement having a highly directive characteristic, such as a dipole in combination with a parabolic reflector. Hence, by periodically moving the antenna combination through a closed path, the narrow antenna beam or lobe likewise periodically sweeps through a portion of space and, when a desired signal is received, the direction of the signal source relative to the antenna apparatus is determined by the orientation of the antenna beam or lobe. Lock-on and tracking are thereafter easily achieved by Well-known methods.

Since the antenna apparatus is generally bulky and heavy, as where a large parabolic reflector or dish is utilized, it will immediately be recognized that one of the disadvantages of such an antenna system is that the scan rate is inherently slow. A further disadvantage of such prior art equipment is due to the fact that moving mechanical parts are required and, as is Well known, such parts may be expected to wear relatively quickly with continued use. As a result, accuracy may oftentimes be impaired. Moreover, for the reasons mentioned, periodic examination and replacement of these parts may be necessary, thereby ultimately increasing the cost of such equipment.

Still further, a significant disadvantage of these earlier types of scanning antenna systems is that, in addition to relative bulk and Weight, the movement of the antenna apparatus poses a difficult problem in mounting them into aircraft and other airborne vehicles wherein space availability and weight reduction are of paramount importance.

It is, therefore, an object of the present invention to provide an electronic antenna scan system.

It is another object of the present invention to provide an antenna system that automatically searches for and locks-on to a signal source target.

' his a further object of the present invention to provide an antenna system that electronically scans space without the aid of moving mechanical parts.

The present invention overcomes the above-mentioned and still other disadvantages encountered among prior art antenna scan systems by providing an antenna many which automatically adjusts itself to at all times give maximum antenna field directivity in the direction of the incoming signal. According to the basic concept of the invention, the out-of-phase components of the incoming signal respectively received at the antennas in the array are compared to a reference signal which is derived by linearly and instantaneously adding all the components. As a result of the comparisons, error signals are produced that are used to ultimately bring the individual signal components into phase with the reference signal which correspond to their sum. In consequence thereof, the reference signal, which is also the desired output signal of the array, is a maximum. Thus, by so doing, the antenna system of the present invention is able to build up its directivity in any desired direction and, because of its self adjusting nature, to at all times maintain it properly directed. In the absence of transmitted signals, noise' signals "take over'and cause the directivity of the antenna array to successively build up first in one direction and then in another, thereby providing the desired scan.

In one form of the invention, the comparisons between reference and component signals are made by feeding the signal components out of the antennas to a common summing circuit which, by instantaneously and linearly adding them, produces the reference signal. In addition, the signal component out of each antenna in the array is fed to a phase-locked type of circuit associated with that antenna. The reference signal is also applied to all phase-locked circuits wherein the phase comparisons previously mentioned take place. The error signals produced in response to these comparisons are then employed to correctively phase shift the antenna signal components until they are in phase with each other and the summing circuit output is a maximum. At this point, the error signals are reduced to zero. Should any changes occur in the position of the signal source, the cycle briefly described above is then reactivated until maximum output or, stated differently, maximum and properly oriented directivity, is once again attained. Tracking is achieved in this way.

It should be apparent that no moving mechanical parts are utilized in the present invention and that it is not subject, therefore, to any of the disadvantages associated with their use, as encountered in the prior art. Furthermore, since the system of the present invention is electronic in nature, it is inherently of small size and weight as compared to earlier systems, especially in view of the fact that it lends itself to miniaturization techniques as does most electronic apparatus. As a result, the present invention makes a very material contribution to the space and weight problems faced in the aircraft, satellite and missile fields. Finally, it should be mentioned again that a significant advantage of the present invention is that at Whatever direction a signal is received, the antennas in the array would automatically become properly phased to maximize the received energy and track the source of the signal.

The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description considered in connection with the accompanying drawings in which several embodiments of the invention are illustrated by way of example. It is to be expressly understood, however, that the drawings are for the purpose of illustration only and are not intended as a definition of the limits of the invention.

FIG. 1 is a block diagram of one embodiment of an electronic antenna scanning system according to the present invention;

FIG. 2 is a block diagram of a modification to the embodiment of FIG. 1;

FIG. 3 is a block diagram of another embodiment of an electronic antenna scanning system according to the present invention; and

FIGS. 4(a), 4(1)), "and 4(a) are block diagrams of possible modifications to the embodiment of FIG. 3.

Referring now to the drawings, there is shown in FIG. 1 one embodiment of an antenna system which, in accordance with the present invention, automatically and continuously searches for a signal source and, once having found it, thereafter adjusts itself to lock onto and track the source.

A basic arrangement of this embodiment is shown in FIG. 1 and is seen to include a pair of antennas a and 10b which are respectively coupled to a pair of phaselocked type of networks, generally designated 11a and 11b, which may also be looked upon as a pair of servomechanism loops.

Network 11a comprises phase-shifter and phase-detector circuits 12a and 13a, respectively, each circuit having a pair of input terminals, and also comprises a low-pass filter 14a which is connected between the output end of the phase detector and the second input terminal of the phase shifter. Antenna 10a is coupled to the first input terminal of phase shifter 12a whose output end, in turn, is connected directly to the first input terminal of phase detector 13a. In a similar manner, network 11b comprises phase-shifter and phase-detector circuits 12b and 1317, respectively, each of which also has a pair .of input terminals, and a low-pass filter 14b. As before, filter 14b is connected between the output end of the phase detector and the second input terminal of the phase shifter to whose first input terminal antenna lllb is coupled. As

expected the output end of phase shifter lzb is connected directly to the first input terminal of phase detector 13b.

The antenna system further includes a summing circuit 15 having a plurality of input terminals so that a number of signals may be linearly added by the circuit. In the arrangement of FIG. 1, two of the circuits 'input terminals are respectively connected to phase shifters 12a and 12b to receive the output signals therefrornp A narrow-band filter and limiter network 16 are connected between summing circuit 15 and a 90 phase-shifter circuit 17 whose output is fed to the first input terminals of both phase detector 13a and phase detector 13b. The output of the antenna system as a whole is taken from the output end of summing circuit 15 and may be connected to a receiver designated 18 orsome other utilization circuit.

In considering the operation, it'will'first be assumed that a signal from some distant source is being received and that it is coming in at some angle determined by the plane in which the antennas are positioned and the location in space of the signal source relative to the system. It will be recognized by those skilled in theart that because of the angle of arrival, the incoming signal will be intercepted by one antenna before the other and that, in consequence thereof, the signal developedat the output leads of the two antennas will be out of phase with each other by an angle The phase angle between the induced signals will, of course, depend upon the spacing between antennas 10a and-10b and the angle'of arrival of the incoming signal.

Accordingly, upon receipt of the incoming signal,'two signals of substantially equal amplitude but out of phase with each other are respectively induced in antennas 10a and 10b and thereafter applied to phase shifters 12a and.

1217. At this point it will further be assumed for the sake of simplicity and clarity that initially phase shifters 12a and 12b have different settings, which is to say, that the general case is assumed in which the phase shifters I phase shifters 12a and 12b are'respectively'i passed them both'to phase detectors 13a and ISb-andsuinming the signal out of phase shifter 12b is simultaneously applied to the first input to phase detector 13b and to an- FIG. 1 is to bring all these signals into phase with each other.

Accordingly, the output signal produced by summing circuit 1-5 is applied to and passed by narrow-band filter and limiter 16, the passed signal then being applied to 90 phase shifter 17 which, as the name implies, shifts the phase of the output signal by 90. The filtering and limiting are for discrimination against noise and amplitude modulation whereas the 90 phase' shift is introduced to maintain thephase around'network loops 11a and 11b at zero degrees since the :point of control in phase discriminators 13a and 13b for zero error signal output is where the two inputs to each discriminator are 90 apart in phase.

The phase shifted output signal produced at the output of circuit 17 is simultaneously applied to the second input terminals of phase discriminators 13a and 13b and since this signal is out of proper phase with the signal applied to the first input terminal of discriminator 13a and out or proper phase as well with thesignal applied to the first input terminal of discriminator 13b, an error signal is produced at the output of each .of them. However, it will be recognized that the polarity of the error signal produced by phase discriminator 13 is opposite that of the error signal produced by phase discriminator 13b. Thus, if one error signal is positive, the other is negative. i

It is thus seen that the error'signals, after being passed through low-pass filters 14a and 14b, will affect phase shifters 12a and llbdifferently, .the'error signal out of phase discriminator'lSa causing the phase angle between its two input signals to be-reduced to 90 and the error signal out of phase'discriminator 13b causing the phase angle between its two input signals to be increased to 90; Ultimately this will happen and in a very short time and when it does, the signals out of phase shifters 12a and 12b will be in phase with each other and in phase also'with the signal out of summing circuit lS. At this point, the effective directivit'yof the system" will be greatest in the direction-of the signal source and the antenna gain for the :system will be at a maximum. It is thus seen how, in the manner described, the system will automatically phase itself to maximize received energy and track the source of it irrespective of the direction from which itcomes; V 1 The verbal explanation of theioperation as presented above may be mathematically reinforced as follows:

Signal out of antenna 12a=E sin wt Signal "out of antenna 12b=E sin (wf+) where, V V

21 rb'sin'fi s V V a b being the baseline distancebetween the antennas, A being the wavelength of the incoming signal, and 13 is theangle of arrival of the wave measured from the i baseline to the baseline normal.

" Accofdinglyflhe signal out of phase: shifter 12a is' circuit 1'5, the signal out of phaseshifter 12a simultaneously being applied to the first input'to phase detector 13a and one of the inputs to summing circuit 15 whereas E inf ict-1 0 and the signal out' of phaseshifter 12!) is V I iEsin w:+ +a

where, 0 and 0 are theJ -initial settings of 'the phase shifters. V

Adding the two signals together, the signal E out of summing circuit 15 is:

s= 1) 2)l By trigonometry,

This represents a signal of amplitude 2E cos /2 (0 --0 and a phase angle of The amplitude will obviously be a maximum when With this value of the phase angle of E out of circuit 15 is The system array may include a larger number of antennas by appropriately connecting in additional antennas and associated phase-locked circuits. The manner in which additional antennas and associated circuitry may be connected into the system is clearly shown by the circuit blocks presented between antennas 10a and 10b and net works 11a and 11b in the figure. It will be recognized that by the further addition of antennas, the directivity and gain of the system may be further improved.

It should also be noted that although the system of FIG. 1 is designed solely for the reception of signals, it may be modified to accommodate the transmission of signals as well, such transmissions being made with the same high directivity and antenna gain attained for signal reception. Such a result may be accomplished by connecting a gating circuit, which may be a T-R switch type of device, between the low-pass filter and the variable phase shifter in each of the phase-locked circuits. Reference is made to FIG. 2 wherein such a gating circuit, designated 19a, is shown connected in phase-locked circuit 1111. Also shown in FIG. 2 is a transmitter-receiver 20 to which gating circuit 19a is directly connected. Other gating circuits in other phase-locked circuits would be connected in the same manner.

In operation, when signals are being received from some distant source, the gating circuits are in an On condition so that signals out of low-pass filters 14a and 14b are passed to phase shifters 12a and 12b. On the other hand, when the receiver portion of transmitter-receiver 20 is turned Off and the transmitter portion simultaneously turned On, a pulse is generated in so doing that is applied to the gating circuits, thereby placing them in an Otf condition so that so signals are passed through them to the phase shifters. Consequently, the directivity and antenna gain of the system remain fixed at the levels attained during reception so that maximum energy is transmitted toward the signal source from which the signals were previously received. In the event that additional antennas are employed in the system beyond the two shown in FIG. 1, then it will be obvious that a gating circuit is to be included in each of the phase-locked circuits associated with these additional antennas.

Having thus described one embodiment of the invention and a modification thereof, reference is now made to another embodiment as shown in FIG. 3. As shown, this embodiment includes a pair of antennas 30a and 30b respectively coupled through a pair of mixer circuits 31a and 31b to both a summing circuit 32 and a pair of phaselocked circuits, generally resignated 33a and 33b. More specifically, antenna 30a is connected to a first input terminal of mixer 31a, a voltage-controlled oscillator 34a being connected to the second input terminal of the mixer. The output end of mixer 31a is connected to the first of two input terminals to a phase-detector circuit 35a and is also connected to one of several inputs to summing circuit 32. Phase detector 35a is coupled at its output end through a low-pass filter 36a to the input end of the abovesaid voltage-controlled oscillator. Similarly, antenna 30b is connected to the first input terminal of mixer 31b, the second input terminal of this mixer being connected to the output end of a voltage controlled oscillator 34b. A phase detector 35b and a low-pass filter 36b complete the loop of phase-locked circuit 33b, filter 36b being connected between the output end of the phase detector and the input end of the voltage controlled oscillator. The output end of mixer 31b is connected both to the first of two input terminals to phase detector 35b and to another of the input terminals to summing circuit 32..

Summing circuit 32 is connected at its output end to a narrow-band filter 37 which, in turn, is connected at its output end to another phase-locked circuit which is generally designated 38. More particularly, phase-locked circuit 38 includes a phase detector 39, a low-pass filter 40 and a voltage-controlled oscillator 41 connected in a loop, the phase detector having two input terminals and being connected at one of these terminals to the output end of filter 37 and at the other of these terminals to the output end of oscillator 41, the detector being coupled at its output through low-pass filter 40 to the input end of oscillator 41. Finally, the junction between phase detector 39 and voltage-controlled oscillator 41 is connected to the second input terminals of phase detectors 35a and 35b, while the output of summing circuit 32 is connected to a receiver 42 or some other utilization devices.

In operation, when a signal at frequency f is intercepted by antennas 30a and 30b, the signal out of antenna 30a is applied to the first input to mixer 31a and the signal out of antenna 30b is applied to the first input to mixer 31b. At the same time, signals generated at frequency f by voltage-controlled oscillators 34a and 34b are respectively applied to the second inputs to mixers 31a and 31b. Each of the mixers heterodynes the signals applied thereto to produce a signal at a frequency f which may be either the sum or diiference between frequencies f and i in this case preferably the dilference frequency. Due to the fact that the signals out of antennas 36a and 30b are out of phase with each other, for the reasons previously mentioned, and due to the further fact that the signals generated by voltage-controlled oscillators 34a and 34b are in all probability out of phase with each other, it will be readily accepted that the signals produced by mixers 31a and 31b are also out of phase with each other initially.

The mixer signals are applied to summing circuit 32 wherein they are instantaneously added to produce a resultant output signal that is passed by band-pass filter 37 to the first input to phase detector 39. It will be recognized by those skilled in the electronic arts that the phase of the output signal produced by summing circuit 32 is intermediate those of the mixer signals, that is to say, the signal out of circuit 32 lags one of the signals out of mixers 31a and 31b and leads the other. To the second input to phase detector 39 is applied the signal generated by voltage-controlled oscillator 41, which is also at frequency f Consequently, detector 39 compares the phases of the two signals applied to it and, in response thereto, produces an error signal whose amplitude and polarity are determined by the relative phase difierence between the signals. This error signal is filtered by low-pass filter 40 and thereafter fed back to oscillator 41 which is adjusted thereby to shift the phase 7 of its signal in such a manner as to reduce the difference in phase between its signal and the signal from the summing circuit. Of course, this process also has the effect of reducing the error signal which will be reduced to zero when the mentioned signals are brought into phase agreement. This result is ultimately obtained.

At the same time that the signals produced at the outputs of mixers 31a and 31b are applied to summing circuit 32, they are also respectively applied to phase detectors 35a and 35b at the first inputs thereof. The signal generated by voltage-controlled oscillator 41, on the other hand, is applied to the second inputs to phase detectors 35a and 35b. The phase detectors compare the phases of the signals applied to them and, in response thereto, they produce error signals that are respectively smoothed by low-pass filters 86a and 36b and thereafter applied to voltage-controlled oscillators 34a and 3412. As before, the amplitude and polarity of each error signal is determined by the relative phase difference between the signals applied to the associated phase detector. From what was previously said with respect to the rela tive phasing of the signals out of summing circuit 32 and mixers 31a and 31b, it will be obvious that the two error signals are of opposite polarity, that is, if one is positive then the other is negative.

The mentioned error signals cause a shift in the phase of the signals generated at frequency f by voltage-controlled oscillators 34-a and 34b and, as a result of this shift in phase, the two signals respectively produced by mixers 31a and 31b at frequency f are brought somewhat more into phase with each other, that is, the phase angle between them is reduced. This, of course, is reflected in a phase shift of the signal generated at frequency f by voltage-controlled oscillator 41 which, in turn, causes further phase shifting of the oscillator 34a and 34b signals. In consequence, the phase difference between the signals out of mixers 31a and 31b is still further reduced. This cycle continues until the mixer signals are in phase with each other which means that the output signal produced by summing circuit '32 and applied to receiver 42 is of maximum amplitude. At this point, all error signals are at zero level so that the antenna system remains fixed in this condition of maximum directivity and gain. However, should the signal source change its position relative to the system, then-the system will readjust itself in the manner described to again provide a maximum output signal or, stated differ: ently, maximum directivity and gain. In this way, the signal source is tracked.

In the event that no transmitted signal is received, then noise signals will governthe system as mentioned in connection with the embodiment of FIG. ,1 and the system will hunt or search, the directivity of the system being built up first in one direction and then in another, thereby providing a scan of the skies. When. a signal does then appear on the scene, the system locks-on to the signal as described.

Here again, although only two antennas and their associated'circuitry were described as being included in the embodiment of FIG. 3, it will be recognized that the system may be enlarged to increase its directivity and gain by adding additional antennas and circuits to it. The addition of one antenna and its associated circuitry is shown "in FIG. 3 by the circuit blocks between antennas Sim-and b and networks 33a and33b. The manner in which the additional antenna arrangement. is connected into the system is clearlyillustrated. Any further additions would be similarly connected.

Referring now to FIG. 4, several ways are illustrated therein for modifying the embodiment of FIG; '3' to provide for both transmission and reception with maximum directivity and gain. This may beiachieved by connecting any one of the circuits of'FIGS. 4a,-4b' or' 40 bei f 3 simplicity, onlyone antenna, oscillator andmixer of the system, namely, antenna 30a, voltage controlled oscillator 34:: and mixer 31a are used for illustrative purposes.

Considering FIG. 4a first, the modification consists of connecting an amplifier 50a and attenuator 51a in series between oscillator 34a and mixer 31a, the amplifier being connected to the oscillator and the attenuator to the mixer. The function of attenuator 51a is to reduce the output power level of amplifier 50a to' the output power level of oscillator 34a so that mixer 31a will not be overloaded during a period of signal reception. A manually operable phase shifter, called a phaser herein and designated 52a, is connected between the output of amplifier 50a and the [first of the inputs to a mixer 53a, the second mixer input being connected to the transmitter output of a transmitter-receiver 54. Transmitter-receiver 54, it will be recognized, is common to all antenna circuitry in the system. A T-R (transmit-receive) switch 55a is connected between antenna 30a and mixer 31a as well as between mixer 53a and transmitter-receiver 54. During signal reception, T-R switch 55a will admit signals from antenna 30a to mixer 31a but will not permit any signals to be passed to the antenna from mixer 53a. Accordingly the operation is the same as that pre-' viously described for the system of FIG. 3 with the exception that the signal out of voltage-controlled oscillator 34a is first amplified and then attenuated before being applied to mixer 31a. However, in all other respects the operations are the same sothat the system ultimately adjusts itself to provide maximumdirectivity and gain.

In order to transmit tothe distant signal source, the receiver portion of transmitter-receiver 54 is turned off and, simultaneously therewith, the transmitter portion is turned on. When this is' done, the switch by which the changeover is accomplished is instrumental in applying a pulse to T-R switch 55a which, in response to the pulse, thereafter prevents signals'from antenna 30a from passing to mixer 31a but allows signals from mixer 53a to be passed to the antenna instead. Taking mixer 31a out of the systern'fixes the phase of the signal generated by voltage-controlled oscillator 34a with the result that the directivity and gain of the system likewise remain fixed during the transmission period.

Briefly, the signal generated by oscillator 34a at frequency f is first amplified by amplifier 59a and then applied to phaser 524 by means of which any phase shifts experienced by the oscillator signal in passing through the amplifier and attenuator 51a are compensated in that the phaser equalizesthe phase of the signals out of attenuator 51a and. phaser 52a. After passing through phaser 520, the oscillator signal is applied to the first input terminal of mixer 53a'which heterodynes this signal against the transmitter signal applied to the second input terminal of the mixer. The transmittersignal is preferably generated at frequency f Consequently, thesignal produced by mixer 53a is at frequency f the frequency of the signal received from the distant source. The mixer output is applied through T-R switch 55ato antenna 30a which radiates the signal toward the source; As mentioned before, the antennas in the system taken as a whole radiate with the same peak directivity and gain as was attained during reception.

Due to the fact that during reception the signal out of oscillator 34a is first amplified and then attenuated before' being applied to mixer 31a, a powerless issustained that is preferably avoided and it may be avoided by simplifying thearrangement of FIG. 4a to that shown inFIG. 4c. In essence,; attenuator 51a haslbeen taken out of the system'and amplifier Elia has been inserted between phaser 52a and mixer 53a, 'llhus, oscillator 34a is connected directly to mixer 31a as it is in the arrangetween each antenna, voltage-controlled oscillator and mixer in the system offiFIG. 3. However, for sakeof '75 ment of FIG. 3. As forfthe operation, the operation of the arrangement of FIG..4c.is;basically the same as the operation of'the arrangement of FIG. 4a. Hence, no de.

tailed discussion of the operation is deemed necessary here.

i In the arrangements of 568. 4a and 4c, compensation for phase shifts introduced by amplifier 50a and which may cause some deviation from optimum directivity and gain were made manually by phaser 52a. Such compensation can be made automatically by replacing phaser 52a with a variable phase shifter 56a, a phase detector 57a and a 90 phase shifter 58a, as is shown in FIG. 4b. Variable phaser shifter 56a is connected between voltagecontrolled oscillator 34a and amplifier 50a, whereas phase detector 57a is respectively connected at its two inputs to amplifier 50a and 90 phase shifter 58a. The output end of the phase detector is connected to an input of variable phase shifter 56a while the input end of the 90 phase shifter is connected directly to the output of oscillator 34a.

In operation, when a signal is being received, the signal is passed through T-R switch 55a to mixer 31a and the cycle previously described in connection with the system of FIG. 3 takes effect, the ultimate result being the building up of the directivity and the gain of the system until it is optimum in the direction of the signal source. On the other hand, when transmitter-receiver 54 is switched over to the transmitter, a pulse is simultaneously generated which is applied to T-R switch 55a. In response to this pulse, the T-R switch prevents the further passage of received signals to mixer 31a but allows instead the passage of signals from mixer 53a, which are then radiated with the relatively high level of directivity and gain previously attained.

Accordingly, the signal generated by voltage-controlled oscillator 34a at frequency i is amplified by amplifie 50a and then heterodyned in mixer 53a against the signal generated by the transmitter at frequency f The resultant mixer output signal is at frequency f and this signal passes through the T-R switch to antenna 30a whereat it is radiated toward the distant signal source. T correct for any phase shifts introduced by amplifier 50a and which may decrease the directivity and gain of the system, phase detector 57a in essence compares the phases of the signals but of oscillator 34a and amplifier 50a and if they are not the same then the detector produces an error signal which causes variable phase shifter 56a to automatically adjust itself to suitably phase shift the oscillator signal and thereby bring the two signals into phase agreement. The use of the phase detector loop for phase adjustment has been heretofore described.

It might be desirable to inactivate amplifier 50a or merely turn it down during the period of signal reception. To accomplish either, a pulse may be applied to the amplifier from transmitter-receiver 54, as indicated by dashed line 59a, the pulse being generated when the receiver is turned on. It may be desirable at times to merely turn down or decrease the output level of the amplifier so that the phase correction loop of phase detector 57a will be operative even during reception. In this way, the output of amplifier 50a will at all times be in substantial phase agreement with the output of oscillator 34a and a sharp surge or transient condition is avoided when the transmitter is put into operation.

As was mentioned before, the arrangements in FIGS. 4a, 4b and 4c show the modifications for only one antenna network in the over-all system. Accordingly, each antenna in the system of FIG. 3 must be modified in any one of the ways shown in these figures if the system is to be adapted for the transmission as well as the reception of signals with high directivity and gain.

. {It should also be noted that the antenna system of the present invention has many beneficial aspects to it in addition to the ones mentioned above. Thus, for example,

. it is well known that the impedances of antennas in an array may change with ageing or under different weather sired phase relationship between the signals feeding or received from the antennas in the array. The same detrimental efiect could be produced where the transmission lines coupled to the antennas are of unequal length. The present invention could be used to calibrate out the deviations thusly produced.

Another beneficial feature of the present invention is that it permits antennas in an array to be staggered or, stated differently, positioned one behind the other, while at the same time obtaining the optimum in directivity and gain where this could not normally be achieved.

Having thus described the invention, what is claimed as new is:

1. An antenna system comprising: first and second antenna means for intercepting a signal from a distant signal source and respectively producing first and second signals in response thereto; means for adding together said first and second signals in order to produce a single reference signal therefrom, said means being coupled to receive said first and second signals; and first and second networks respectively coupled to said first and second antenna means and to said means for respectively comparing the phase of said reference signal with the phases of said first and second signals, said first and second networks respectively including first and second circuits for producing first and second error signals whose amplitudes and polarities respectively correspond to the phase differences between said first and second signals and said reference signal, said first and second networks respectively further including first and second additional circuits responsive to said first and second error signals for shifting the phases of said first and second signals until they are in phase with said reference signal, whereby they are in phase with each other.

2. An antenna system comprising: first and second antenna means for intercepting a signal from a distant singal source and respectively producing first and second signals in response thereto; a network for adding together said first and second signals in order to produce a single reference signal therefrom, said network being coupled to receive said first and second signals; and first and second phase-locked circuits respectively coupled to said first and second antenna means and to said network for respectively comparing the phase of said reference signal with the phases of said first and second signals to produce first and second error signals whose amplitudes and polarities respectively correspond to the phase angles between said reference and said first and second signals, said first and second phase-locked circuits respectively including first and second means responsive to said first and second error signals for shifting the phases of said first and second signals until they are in phase with said reference signal, whereby said first and second signals are in phase with each other.

3. An antenna system comprising: first and second antenna means for intercepting a signal from a distant signal source and respectively producing first and second signals in response thereto; a summing circuit coupled to said first and second antenna means for instantaneously adding said first and second signals to produce a single output signal; and first and second phase-locked circuits respectively coupled to said first and second antenna means and to said summing circuit for comparing the phase of said output signal with the phases of said first and second signals to produce first and second voltages whose amplitudes and polarities are respectively determined by the phase differences between said output and said first and second signals, said first and second phaselocked circuits respectively including first and second phase-shifting networks responsive to said first and second voltages for respectively shifting the phases of said first and second signals until they are in phase with said output signal, whereby the system is receiving the signal from the source with optimum directivity and gain.

4. In a transmitter-receiver system, an antenna system that automatically adjusts itself to provide optimum directivity and gain, said system comprising: first and second antenna means for intercepting a signal from a distant signal source and respectively producing first and second signals in response thereto; a summing circuit coupled to said first and second antenna means for instantaneously adding said first and second signals to produce a system output signal; first and second phase-locked circuits respectively coupled to said first and second antenna means and to said summing circuit forshifting the phases of said first and second signals until they are in phase with said output signal, whereby the directivity and gain of the antenna system is optimum; and means in each of said first and second phase-locked circuits for fixing the phases of said first and second signals to provide continued optimum directivity and gain.

-5. In a transmitter-receiver, an antenna system that automatically adjusts itself to provide optimum directivity and gain, said system comprising: first and second antennas for intercepting a signal from a distant signal source and respectively producing first and second signals in response thereto; a summing circuit for instantaneously adding signals appliedthereto to produce a single output signal whose amplitude is a function of the differences in phase between the applied signals;-first and second variable phase shifters respectively connected 7 between said first and second antennas and said summing circuitfor passing said first and second signals to said summing circuit, said phase shifters being operable in response -to first and second voltages respectively applied thereto to shift the phases ofsaid first and second signals inaccordance with the amplitudes and polarites of said voltages; firstancl second phase detector means coupled between the input and output ends of said summing circuit for comparing thephase of said output signal with the phases of said first andsecond signals, said first and second phase detector means being operable in response to said comparedsignals to produce first andsecond voltages whose amplitudes and polarities respectively correspond-to the diiferences in phase between said compared signals, said first and second phase detector'means being respectively connected tosaid first and'second variable phase shifters for applyingsaid first and second voltages thereto, said phase shifters shifting the phases of said first and second signals until they are in phase with said outputisignal, whereby optimum directivity and gainare provided.

-6. The antenna system defined .in claim wherein a firstswitch device is connected between said first phase detector means andsaid first variable phase shifter and a second switch device is connected between'said second phase detector means and said second variable; phase shifter, said first and .second switch devicesbeing connected to the transmitter-receiver and operable therefrom to prevent said first and second voltages from being appliedto said first and second phase shifters, respectively, thereby fixing the phases of said first and second signals to provide continued optimum directivity and gain. 7

7. In a transmitter-receiver system, an antenna system thatautomatically adjusts itself to provide optimum directivity and gain,said system comprisingi first and second antenna means for intercepting a signal from .a distant signalsource and respectively producing first and second signals in responsethereto; a summing circuit coupled to said first and second antenna means for instantaneously adding said first and second signals to produce an output signal whose amplitude is a function of the phase differ-1 ence'between said first andsecond'signalsgand first, second .andthirdphase-locked circuits for making the am: plitude of saidoutput signal a maximum by bringing said first and second signals into phase agreement, said first phasedocked circuit being connected to said first antenna means and tothe input end of said summing circuit, said second phase-locked circuit'being connected to said second;antenna means and to the inputend of said-summing" circuit, and said third phase-locked circuit being-connected between said first and second phase-locked circuits and to the output end of said summing circuit, said first, second and third phase-locked circuits varying said first, second and output signals, respectively, until they are all in phase with each other, whereby optimum directivity and gain is provided.

8. The antenna system defined in claim 7 wherein first and second gating means are coupled between said first and second phase-locked circuits and said first and second antenna means, respectively, and coupled tothe transmitter-receiver, said first and second gating means being selectively operable in response to signals from the transmitter-receiver to simultaneously decouple said summing circuit from said first and second antenna means to fix the directivity and gain of the antenna system at optimum and couple the transmitter to said first and second antenna means for transmitting signals with optimum gain in the direction of the distant signal source.

9.- In a transmitter-receiver system, an antenna system that automatically adjusts itself to provide optimum directivity andgain, said system comprising: first and second antennas for intercepting a signal at frequency f from a distant signal source and respectively producing first and second signals at frequency f in response thereto; first and second voltage-controlled oscillators for respectively generating third and fourth signals at frequency f the phase of said third and fourth signals being affected by the amplitude and polarity of voltages respectively applied to said oscillators, first and second mixer circuits respectively coupled to said first and second antennas and said first and second voltage-controlled oscillators, said first and second mixer circuits being operable in response to said first, second, third and fourth signals to respectively produce fifth and sixth signals at frequency f the phase of said fifth signal being determined by the phases of said first and third signals and the phase of said sixth signal being determined by the phases of said second and fourth signals; a summing circuit for instantaneously adding said fifth and sixth signals to produce a single output signal at frequency f;, whose amplitude is a function of the phase difference between said fifth and sixth signals; a third voltage-controlled oscillator for generating a local signal at frequency f the phase of said local signal being affected by the amplitude and polarity of a voltage applied to said third oscillator; a third phase detector 7 v coupled between said summing circuit and said third volt- I age-controlled oscillator and operable in response to said output and'local signals therefrom to produce a third voltagewhoseamplitude and polarity corresponds to the phase difference between saidoutput and local signals; a third ilow-pass filter connected between said third phase detector and said third oscillator, said third filter smoothing'said third voltage and vthereafter. applying it to said third oscillator which,gin response thereto, shifts the phase of said local signaluntil it is in phase with said 7 output signal; first and second phase detectors connected between said first and-second mixer circuits,'respectively, and said third voltage-controlled oscillator, said first and second phase detectors being operable in response to said fifth and sixth signals and said local signal to respectively produce first and second voltages whose amplitudes and polarities correspond tothedifferences in phase between the signals applied to the'respe'ctive phase detectors; first and second low-pass filters connected between said first and second phase detectors and said first and second voltage-controlled oscillators, respectively, said first and second filterssmoothing said first and second 1 voltages and thereafter' respectively applying them to said first and second oscillators which,-in response thereto, shift the phases of said third-and fourth signals until said fifth and sixthsignals are, in phase with said local signal, wh'ereby-the amplitude of said output signal isa maximum and optimum idire ctivity and, gain is, provided.

i 10. The; antenna system d afinedcin claim ,9 wherein I v 13 I first and second switching means are connected between said first and second antennas and said first and second mixer circuits, respectively, and respectively coupled to said first and second voltage-controlled oscillators, said first and second switching means being selectively oper able in response to signals from the transmitter-receiver to decouple said first and second antennas from said first and second mixer circuits to prevent said first and second signals from being passed thereto, thereby fixing the directivity and gain at optimum, said first and second switching means being coupled to the transmitter-receiver and operable in response to the signals therefrom to couple the transmitter to said first and second antennas for transmitting signals in the direction of the distant signal source with maximum gain.

11. The systemdefined in claim wherein said .first and second switching means each includes an amplifier and attenuator connected in tandem between the associated voltage-controlled oscillator and mixer circuit, said attenuator being adjusted to reduce the power level of the amplifier output to the power level of the oscillator output, a transmit-receive switch connected between the associated antenna and mixer circuit and connected to the transmitter-receiver, a phaser connected to said amplifier for calibrating out phase shifts produced by said amplifier in the oscillator output signal, and a mixer circuit connected between said phaser and said transmitreceive switch and to the transmitter, said mixer heterodyning a signal generated at frequency f by the transmitter against the signal out of said phaser at frequency i to produce a signal at frequency f for transmission through said transmit-receive switch for radiation into space by said associated antenna.

12. The system defined in claim 10 wherein said first and second switching means each includes a transmitreceive switch connected between the associated antenna and mixer circuit and to the transmitter-receiver, and a phaser, amplifier and mixer circuit connected in tandem between the associated voltage-controlled oscillator and said transmit-receiver switch, said phaser being operable to calibrate out phase shifts produced by said amplifier in the oscillator output signal, said mixer circuit being connected to the transmitter and being operable to heterodyne a signal at frequency f generated by the transmitter against the signal out of said amplifier at frequency f to produce a signal at frequency f for transmission through said transmit-receive switch for radiation into space by said associated antenna.

13. The system defined in claim 10 wherein said first and second switching means each includes a transmit-receive switch connected between the associated antenna and mixer circuit and to the transmitter-receiver, an amplifier for amplifying the associated voltage-controlled oscillator signal at frequency f a phase-locked circuit connected between said amplifier and associated oscillator for automatically calibrating out any phase shifts introduced by said amplifier in said oscillator signal, and a mixer circuit connected between said amplifier and said transmit-receive switch and to the transmitter, said mixer being operable to heterodyne a signal at frequency f; generated by the transmitter against the signal out of said amplifier at frequency f to produce a signal at frequency h for transmission through said transmibreceive switch for radiation into space by said associated antenna.

14. An antenna system comprising: first and second antenna means for intercepting a signal from a distant signal source and respectively producing first and second signals in response thereto; means for adding together said first and second signals in order to produce a single reference signal therefrom, said means being coupled to receive said first and second signals; and first and second networks respectively coupled to said first and second antenna means and to said means for respectively comparing the phase of said reference signal with the phases of said first and second signals, said first and second networks 14 respectively including first and second circuits operable to shift the phases of said first and second signals and, thereby, of said reference signal until all of said signals are in phase with each other.

15. Apparatus for optimizing an output signal obtained from first and second signals applied to the apparatus which comprises: means for adding the first and second signals in order to produce the output signal, said means being coupled to receive the first and second signals; and first and second networks coupled to respectively receive the first and second signals and coupled to said means for comparing the phase of the output signal with the phases of the first and second signals, said first and second networks respectively including first and second circuits operable to shift the phases of the first and second signals and, thereby, of the output signal until all of the signals are in phase with each other.

16. Apparatus for optimizing an output signal obtained from first and second signals applied to the apparatus which comprises: a summing circuit for instantaneously adding the first and second signals in order to produce the output signal, said means being coupled to receive the first and second signals; first and second variable phase shifters coupled to respectively pass the first and second signals to said summing circuit, said phase shifters being operable in response to first and second voltages respec tively applied thereto to shift the phases of said first and second signals in accordance with the amplitudes and polarities of said voltages; first and second phase detector means coupled between the input and output ends of said summing circuit for respectively comparing the phases of said first and second signals with the phase of said output signal, said first and second phase detector means being operable in response to said compared signals to produce first and second voltages whose amplitudes and polarities respectively correspond to the differences in phase between said compared signals, said first and second phase detector means being respectively connected to said first and second variable phase shifters for applying said first and second voltages thereto, said phase shifters shifting the phases of said first and second signals until they are in phase with said output signals, whereby an optimum output signal is obtained.

17. An antenna system comprising: a plurality of more than two antenna arrangements for intercepting a wavefront from a distant signal source and respectively producing a corresponding plurality of antenna signals in response thereto; means for adding together said plurality of antenna signals in order to produce a single reference signal therefrom, said means being coupled to receive said plurality of antenna signals; and a plurality of networks respectively coupled to said plurality of antenna arrangements and to said means for comparing the phases of the respective antenna signals with the phase of said reference signal, said plurality of networks respectively including a plurality of circuits for producing a corresponding plurality of error signals whose amplitudes and polarities respectively correspond to the phase differences between the respective antenna signals and said reference signal, said plurality of networks respectively further including a plurality of additional circuits respectively responsive to said plurality of error signals for shifting the phases of said antenna signals until they are all in phase with said referenced signal, whereby they are all in phase with each other.

18. Apparatus for optimizing an output signal obtained from a plurality of input signals, said apparatus comprising: means for adding the plurality of input signals together in order to produce the output signal therefrom, said means being coupled to receive the input signal; and a plurality of networks coupled to respectively receive the plurality of input signals and coupled to said means for comparing the phase of the output signal with the phases of the respective input signals, said plurality of networks respectively including a plurality of circuits that 5.5 are operable to shift the phases of the respective input signals until they are all in phase with the 'outputsignal and, thereby, with each other. I

'19. Apparatus for optimizing an output signal, said apparatus comprising: a summing circuit for instantaneously adding a pluralityof signals applied thereto in order to produce the output signal whose amplitude" ista function of the differences in phase between 'theapplied signals; a plurality of variable phase shifter circuits coupled to respectively pass said plurality of signals to'said summing circuit, said phase shifter circuits being operable in response to error voltages respectively applied thereto to shift the phases of the respective signals in accordance with the amplitudes and polarities of said voltages; a plurality of phase detector means coupled between the input and output ends 'of'saidsumming circuit to respectively compare the phases of said plurality 'of signals with the phase of the output signal, saidplurality of detector means beingoperable in response to said signal, comparisons to respectively produce a plurality of error voltages whose amplitudes and polarities correspond to the differences in phase between said comparedsignals, said plurality of detector means. respectively being connected to said plurality of variable phase shifter circuits for applying said error voltages thereto, said phase shiitcr circuits respectively shifting the phases of said signals 1 3 until they are in phase with the output signal, whereby the outputsignal is optimized.

,20. Apparatus for optimizing an output signal, said apparatus comprising: "means for adding a plurality of N signals 'applied'thereto in order to; produce the output signal whoseamplitude is a function of the differences in phase between the applied signals, N being, an integer greater than 2; a plurality of N+1 phase-locked circuits for making the'amplitude of the output signal a maximum by'bringing said N applied signals into phase agreement, N of said Net-1 phase-locked circuits being coupled to respectively pass said N signals to the input end of said means, the"N|-1st-of-said N+1 phase-locked circuits being coupledbetween said N phase locked'circuits and the output end of'said means, said N phase-locked circuits varying said N signals, respectively, and said N+1st phase locked circuit varying the output signals until they are all inphase with each other.

References Cited'in the file of this patent UNITED STATES PATENTS Adams Mar. 14, 1961 

